1. Field of the Invention
The present invention relates to a projection zoom lens system having a five-group configuration and a projection type display apparatus equipped with the projection zoom lens system. Specifically, the invention relates to a projection zoom lens system and a projection type display apparatus which are suitable particularly in a case where rays containing image information, which are generated from a light valve such as a transmissive or reflective liquid crystal display device or a DMD (Digital Micromirror Device) display device, are projected from the front side and magnified on a screen.
2. Description of the Related Art
Recently, there has been remarkable development of projection type display apparatuses which display image information of a computer, a television, and the like in an enlarged manner by using light valves such as a liquid crystal display device and a DMD display device.
A zoom lens system capable of changing the size of an image is generally used as a lens system provided in such projection type display apparatuses. However, in recent years, the zoom lens system has been required to have a large change rate, that is, a large zoom ratio.
Further, the zoom lens system is also required to have a function (which is a so-called lens shift projection function) of moving an image position far away from the projection type display apparatus during projection of the image and a function of obtaining a large image by projecting the image to a position close to the projection type display apparatus. Hence, the projection zoom lens system is required to achieve an increase in the angle of view.
Furthermore, considering an increase in the precision of the recent light valves itself and the requirements and convenience of a user who uses the apparatus in a small indoor space, the projection zoom lens system is required to achieve high resolution and compactness.
In the projection zoom lens systems having a five-group configuration are disclosed in JP-A-2001-91829 and JP-A-2001-100100, a negative first lens group, a positive second lens group, a positive third lens group, a fourth lens group, and a positive fifth lens group are arranged in order from the magnification side. During zooming, the first lens group and the fifth lens group remain stationary, and the second to fourth lens groups are moved.
Since these known projection zoom lens systems are configured so that the fourth lens group includes negative, positive, negative, positive, and positive lenses arranged in order from the magnification side, fluctuation in various aberrations accompanying the zooming operation is relatively small. In addition, since the fifth lens group is formed of one lens, a relatively compact configuration is achieved.
However, the known projection zoom lens system has a zoom ratio of 1.2 to 1.3 times or so and a total angle of view of 60 degrees or so at the wide-angle end. Thus, the zoom lens system does not comply with the recent requirements.